MAJOR: server: add DNS-based server name resolution

Relies on the DNS protocol freshly implemented in HAProxy.
It performs a server IP addr resolution based on a server hostname.
diff --git a/src/standard.c b/src/standard.c
index 709db8b..4e458c2 100644
--- a/src/standard.c
+++ b/src/standard.c
@@ -25,6 +25,7 @@
 #include <common/config.h>
 #include <common/standard.h>
 #include <types/global.h>
+#include <proto/dns.h>
 #include <eb32tree.h>
 
 /* enough to store NB_ITOA_STR integers of :
@@ -608,6 +609,9 @@
 	if (!resolve)
 		return NULL;
 
+	if (!dns_hostname_validation(str, NULL))
+		return NULL;
+
 #ifdef USE_GETADDRINFO
 	if (global.tune.options & GTUNE_USE_GAI) {
 		struct addrinfo hints, *result;